This invention relates to wire braiding.
In the manufacture of a variety of products, such as shielded electrical cable and flexible hydraulic and pneumatic housing, wire is tightly woven over a tubular core to form a braided sheath. The wire strands are typically wound on supply bobbins which are driven along sinuous paths in opposing directions around the tubing, passing over and under one another to lay the wire in an interlaced woven pattern over the surface of the tubing. Each supply bobbin is mounted on a carrier which pays out the wire under controlled tension during braiding.
The wire is often wound on the bobbins, and payed out, in multi-strand bundles. Since the wire strands within each bundle are not of precisely the same length, the shorter strands are placed under greater tension during the braiding operation and stretch slightly until the lengths of the strands are equalized. When textile filaments or "soft" wire is braided, considerable elongation under tension is permissible, and tension alone works well to compensate for variations in length among the bundled strands.
However, in the construction of certain products, such as hydraulic hose, it is essential to use "hard" wires having great tensile strength. It is the strength of braided-wire sheath which permits the hose to handle high pressure without bursting. Because hard wire can be stretched very little, even under great tension, braiding tension alone does not adequately eliminate length variations, and the consequent poor distribution of load among the bundled strands significantly reduces the pressure-handling capability of the braided sheath. Moreover, such length variations greatly impede the manufacturing process itself, since excessive slack or broken strands can only be corrected by halting the braiding operation entirely.
It is accordingly the principal object of the present invention to increase the strength and endurance of braided-wire sheath while improving the efficiency of the process for manufacturing such sheath.
In accordance with the invention, the distribution of tension among the bundled strands of high-tensile-strength wire is continually equalized during braiding by passing the bundle through a twisting slot which, when rotated, wraps the slack strands, which are under lesser tension, about the remaining strands which are under greater tension. The cross-sectional area of the twisting slot is greater than the minimum cross-sectional area occupied by the bundle to permit wires under greater tension to move laterally within the bundle relative to wires under lesser tension.
According to a principal feature of the invention, the rotational force applied to the twisting slot is derived from the oscillating motion of the bobbin-carrier as it follows its sinuous course about the tubing core. The twisting slot is formed in a feeding member which is mounted for rotation on the bobbin-carrier. A unidirectional clutch mechanism, such as a ratchet and pawl, allows the feeding member to rotate more freely in one direction than in the other. As the bobbin-carrier follows its sinuous path, its orientation with respect of the direction of wire travel changes, exhibiting a partial rotation first in one direction followed by a return rotation in the other direction. In one direction, the unidirectional clutch urges the feeding member into rotation against the tendency of the twisting slot to align itself relative to the direction of wire travel. The successive incremental rotations of the slot twists the bundled strands. The twisting slot is dimensioned to allow the individual wire filaments within the bundle to realign themselves, the filaments under lesser tension naturally moving to outside of the bundled collection as it is is twisted.